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Friday, April 20, 2018

145Mhz Cross Yagi


2 x 10 el cross yagi 145 MHz. RHCP.
Feed system: adaptation of the dipole in T symmetrical match

The procedure is easy to take all elements and mount them at 90 degree angle on the same boom.
Traditionally circular polarization is generated by feeding two crossed dipoles 90 degrees out off phase. But you can also shift the dipoles 90 degrees in space and feeding then in-phase with the same effect. The advantage is that the two cables in the splitter have equal length and therefore gives identical transformation of antenna impedance
I prefer the mechanical method despite the electrical method (with different length of cable to obtain the 90 deg phase angle). So, I have shifted each V element exactly at ¼ Lambda forward on the boom. So the entire vertical antenna is shifted forward with reference to the horizontal antenna.
The forward shift (Offset) between the two dipoles is 517 mm to obtain 90 deg Phase angle.


Like this the two antennas are excited with a 90 degr. of phase shift. With this now a rotating field is radiated.
By shifting one section of the yagi forward by a quater wavelength the phasing cable to the two antennas becomes equal, impedances becomes equal and the antennas must share the power equally - regardless of the VSWR.
The two antennas must be feed with a splitter. An air line gives by the calculation an impedance of 35,35 ohms : 𝑍𝜆4⁄∗1√𝜀𝑟 =√𝑍𝑝∗𝑍0∗ 1√1 =√25∗50 ∗1= √1250=35,35𝛺
But mechanical splitter is too big at this frequency.
So the splitter can be made from two 75 ohm ¼ lambda equal length of coax cable.
On 144 MHz a quater wavelength coax is 1/4 x 300/144 x 0,66 = 340 mm (the real velocity factor of the coax used must be applied . In this case + 0.66, solid polyethylene dielectric).  I use three quater wavelength 75 ohm cable, which gives the same transformation. The cable length of 102 cm allows the point where the three coax ends are joined together far from the dipoles.
Software: For Yagi antenna, I use the VK5DJ John Drew software ‘’Yagi calculator’’ of http://www.vk5dj.com/yagi.html

 

Sunday, April 15, 2018

Helix antenna 432/435 MHz 14 turns


After my first success with this kind of antenna in 1992 in VE2 land (antenna homemade helix 9 turns) see pic at Blanville, Quebec of my antenna set up, I decided to build another one with 14 turns.
VE2EK Antenna's set-up at Blanville (Quebec)

Wanting to further improve my Satellites antennas after the construction of the portable 2m / 70cm yagi cross, I set about building a 14-turn "Home-made" Helical Antenna for 432/435MHz.

This 50 ohm impedance antenna allows, when fed with 25/50W of SSB RF, to join the 'Molniya' orbiting satellites like AO-40 and AO-10 very easily!
The gain of this antenna is estimated at 16.5 dBd theoretical.
It's all about giving ideas on how to build a sustainable helicoidal antenna, rather than giving you a recipe to follow.

Calculations made with the HelixCalc Software.
Mesured Results with:
- Windfreak SynthNV: 34MHz – 4.4GHz RF Signal Generator/ RF Sweeping/ Power Detector
- Waterbeach Electronics WE-520A 520 Mhz Antenna Analyzer
                           435MHz, VSWR: 1.04/1, Return Loss: 33.17dB
                           433MHz, VSWR: 1.02/1, Return Loss: 40.1dB
                           432MHz, VSWR: 1.01/1, Return Loss: 45.2dB
Bandwith wide and OK for me!!

Note that for the construction of this antenna I chose round metric values;
The diameter of the wire used for the turns and according to ARRL "Antenne Book" should be between 0.006 and 0.05 Lambda.
The following materials were used to build the 14-turn helical antenna:
• Aluminum: 25mm square support, arms reflector supports,
• Teflon PTFE: Spacers
• Galvanized iron: Reflector grid, Bee hive origin !!
• Aluminum: Helical wire (6.35mm (1/4 "dia.) Plumbing pipe
• Stainless steel: All hardware, support.

Notes on the assembly:
• The central support is drilled every 1/2 turns to receive the Teflon PTFE spacers,
• The spacers are drilled for fixing the helical tube at one end. They are also drilled at the other end to be fixed inside the central support.
• Pieces of galvanized wire. are used to fix the turns to the central support in the spacers.
• I painted all steel surfaces with a polyurethane-silicone alkyd paint.
• The coaxial cable used on the antenna is: 10DFB up to the preamplifier. After the preamplifier, Andrew Heliax ½ cable.
• Connector used: Type N, female, panel mount.
• The reflector is designed so that it can be slid on the central support, in order to adjust the TOS. Two screws hold it in place once adjusted.
The final adjustment of the TOS is done by sliding the reflector forwards or backwards. The center pin of connector N, is fixed on the last turn which has a spacing between the back panel ranging from 13mm to 4 mm at the feed point.
**** this antenna can be fixed to the back of the panel with a counter weight or at its equilibrium point on its boom to an isolated support not to disturb the radiation.

See the diagram of the construction:






Saturday, March 24, 2018

HP8648 new toy

Just received my new toy, so so Happy.
I can do something seriously with my updated workbench.
My updated workbench before finding anything else ..


Friday, February 23, 2018

Satellite Yagi crossed 2m, 70cm

Just for fun. Construction of an antenna for experimental satellite communication, 8el. (435 Mhz) x 4el. (145 Mhz) Satellite Yagi crossed.
No difficulty to built this antenna. Except the gamma match that requires a little more attention, but with the informations provided by Alex, XE1MEX, and Rob VK2GOM  (link below) it works very well. Adjustments are easy to adjust.
The bandwidth is very wide on both QRG's.
Without waiting .. Hi, 1st test after adjustments, heard S0-50  59, but duplexer must be checked..(easy to do it).

Almost ready.. ! Not very beautiful, need some improvements for the aesthetic, but the measurements are excellent, So now ... waiting for ISS or a satellites pass above..
I recommend this construction 73 ZS1II

*** 25 Feb 2018 ***Duplexer repaired. The antenna works wonderfully with the Alinco DJ500.  First contact from St Helena Bay locator JF87XF on AO-91 satellite with Tom, ZS1TA and heard many other ZS stations.
Must do fast, pass duration only 11mn...
 
Dipoles are alu pipe dia. 12mm, élements rod alu. dia 6mm, Boom square 20mm

Coax is 10DFB, perfect match in the alu pipe.
Inspired by:
and 
 VK2GOM  Rob – international HAM magazine HAM-MAG April 2010  No 15
A 70cm/2m crossed satellite antenna

04 March 2018 -Simple portable Setup and homemade antenna work fine.
I prefer to use the tripod. It will also be necessary to connect a MP3 recorder because is it not practical to note the call signs, the QSO's, and to hold the antenna to track the Sat's.




Tuesday, January 30, 2018

23cm Interdigital filter

I'm on the way with 23cm station for the EME and the first small filter built in May 2013, did not satisfied me about performance, (1.25 dB loss).
So I decided to built a new one for 23cm band. After some searching on the internet, I found the following drawing of an interdigital filter from Daan PA4DAN.
http://pa4dan.nl/ham/homebrew/23cm_filter/

As I get a lot of aluminum parts, After a quick look in the garage, I found exactly the main piece of aluminum that I needed. Inner section 54 x 28mm.
The rest of the pieces are easy to find.
Hop. Cutting, drilling, tapping and ... settings on the spectrum analyzer.
Surprise! In less than 15 minutes the result are visible on the pic ... beyond my expectations !!
1296.1 Mhz = 0.85 dB, and a very narrow bandwidth.
Look at the picture ...
A nail polish stamped at XYL to block the screws and finished!
I am really happy with this home made construction.


Results of the new one
First Filter
Results of first filter